Hi Norman
- How big is the initial quota of init?
init receives the quota for all the available physical memory from
core.
The amount depends on the physical memory of the machine. It is
printed
by core when init is started.
Thats what I thought. But I couldn't imagine how init's quota could
possibly exceed on a x86-64 machine with several GiB physical memory :)
For each child started by init, init needs to create several
capabilities (e.g., the parent capability presented to the child, or
the
capability for the local ROM session for providing the child's binary
as
"binary" ROM module). The allocation of those capabilities is
performed
via the 'Nova_native_pd::alloc_rpc_cap' RPC function. This function
naturally consumes session quota of the corresponding PD session
(init's
PD session). At one point, the initial session quota (that was passed
to
core when init's PD session was created) is depleted. In this case,
core
prints the diagnostic message and returns an error to the client
(init).
Init responds to this error by upgrading the session quota of its PD
session using the preserved slack memory. The session upgrading is
handled at 'base-nova/src/lib/base/rpc_cap_alloc.cc'.
In your case, the message you see is merely a diagnostic message. The
condition is handled properly. In cases where proper error handing of
the 'Out_of_metadata' condition is missing, the message used to be
quite
valuable to spot the problem. So we decided to kept it.
How can I distinguish if the condition is handled properly or not? Are
there any preceding or following log messages in either case?
- Does the size of the metadata allocation for a child depends on
whether I'm using a 32 or 64 bit system?
Yes. I.e., your scenario produces the message only on 64 bit, not on
32 bit.
Is it worth thinking about calculating the slack memory size based on
Genode::addr_t? Or make the value even configurable?
That said, the limit turned out not to be a problem in your case. The
message is a false-positive warning. The default limit becomes a
problem
not before the PD-session upgrade fails. I can trigger the problem
with
your run script when configuring Qemu with 64 MiB of memory and
starting
76 children. Sorry that my previous email pointed you to the wrong
direction.
It didn't. I'm trying to improve my understanding of memory
configuration and allocation in Genode. So every hint helps ;)
Thanks,
Roman
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